Discrete ADSR
The original circuit was found in the
Music Machines diy-archives.
Its a design by Barry Klein. I started to expand it from
the Original AD-envelope to an ADSR envelope. Make sure you add a 2.2kOhms resistor in series with the
Attack and Decay pots, this prevents clicking and an unwanted latchup condition for the flip-flop.
The second image shows a much simpler ADSR which uses a 555 timer IC to do nearly all what is needed.
It is preceeded by a transistor circuit which buffers the input and generates a short pulse which is needed
to trigger the timer. This is the circuit that I now use, since it has more musical properties.
Unlike the first circuit the attack portion of the ADSR goes immideately to decay when the gate goes low.
In the first circuit the attack (once triggered) goes until the 10V threshold is reached, regardless of
gate going low. This circuit was modified from a circuit from Hal Chamberlins book Musical applications of
microprocessors.
First ADSR Schematic
Second ADSR Schematic